Swan H, Saarinen K, Kontula K, Toivonen L, Viitasalo M
Department of Medicine, Helsinki University Central Hospital, Finland.
J Am Coll Cardiol. 1998 Aug;32(2):486-91. doi: 10.1016/s0735-1097(98)00248-4.
This study investigated the ability of QT duration, QT dispersion (QTD) and clinical diagnostic criteria to correctly identify genetically documented LQT1 type long QT syndrome (LQTS) patients, and to separate symptomatic and asymptomatic LQT1 patients.
Ventricular repolarization has played an essential role both in diagnosis and risk assessment of LQTS. Today, molecular genetic techniques permit unequivocal identification of many LQTS patients.
QT interval and QTD in 12 symptomatic and 18 asymptomatic LQT1 patients and their 43 healthy relatives were evaluated. The sensitivity and specificity of upper normal limits of QT interval, two QT interval adjustment methods (Bazett's and Fridericia's formulas), and the proposed clinical criteria for LQTS were assessed. Occurrence of a mutant (D188N) KVLQT1 gene was considered as the basis of classification into affected and nonaffected individuals.
Diagnostic sensitivity and specificity values were 90% and 88% using Bazett's formula, and 80% and 100% using Fridericia's cubic root formula or upper normal limits for QT interval. Suggested diagnostic criteria for LQTS reached 100% specificity, but 47% of the DNA-documented LQT1 patients were classified into the category of low or intermediate probability of LQTS. QT interval and heart rate did not differ between symptomatic (464 +/- 47 ms, 70 +/- 9 min(-1)) and asymptomatic 460 +/- 41 ms, 65 +/- 13 min(-1)) LQT1 patients. QTD was increased in symptomatic LQT1 patients compared to unaffected relatives (66 +/- 48 vs. 37 +/- 15 ms, p = 0.02), but symptomatic patients LQT1 did not differ from asymptomatic (45 +/- 19 ms).
Not all LQT1 patients can be distinguished from healthy relatives by assessment of QT duration or clinical criteria. Presence of LQT1 gene can carry the risk of cardiac events even with no or only marginal prolongation of QT interval.
本研究调查了QT间期、QT离散度（QTD）及临床诊断标准正确识别基因确诊的LQT1型长QT综合征（LQTS）患者以及区分有症状和无症状LQT1患者的能力。
心室复极在LQTS的诊断和风险评估中均发挥着重要作用。如今，分子遗传学技术能够明确鉴定许多LQTS患者。
对12例有症状和18例无症状LQT1患者及其43名健康亲属的QT间期和QTD进行评估。评估了QT间期正常上限、两种QT间期校正方法（Bazett公式和Fridericia公式）以及LQTS的拟议临床标准的敏感性和特异性。将突变（D188N）KVLQT1基因的出现作为将个体分为受影响和未受影响的基础。
使用Bazett公式时诊断敏感性和特异性值分别为90%和88%，使用Fridericia立方根公式或QT间期正常上限时分别为80%和100%。LQTS的拟议诊断标准特异性达到100%，但47%的基因确诊LQT1患者被归类为LQTS低或中度可能性类别。有症状（464±47毫秒，70±9次/分钟）和无症状（460±41毫秒，65±13次/分钟）LQT1患者的QT间期和心率无差异。与未受影响的亲属相比，有症状LQT1患者的QTD增加（66±48对37±15毫秒，p = 0.02），但有症状LQT1患者与无症状患者（45±19毫秒）无差异。
并非所有LQT1患者都能通过评估QT间期或临床标准与健康亲属区分开来。即使QT间期无延长或仅轻微延长，LQT1基因的存在也可能带来心脏事件风险。
